Spatial monsoon variability with respect to NAO and SO

• Main Authors: Kakade, SB, Dugam, SS
• Format: Article in Journal/Newspaper
• Language: English
• Published: Indian Academy of Sciences 2006
• Subjects: Meteorology and Climatology; Indian; North Atlantic; North Atlantic oscillation
• Online Access: http://moeseprints.incois.gov.in/1937/; http://moeseprints.incois.gov.in/1937/1/Spatial%20monsoon.pdf; http://link.springer.com/article/10.1007%2FBF02702912

In this paper, the simultaneous effect of North Atlantic Oscillation (NAO) and Southern Oscillation (SO) on monsoon rainfall over different homogeneous regions/subdivisions of India is studied. The simultaneous effect of both NAO and SO on Indian summer monsoon rainfall (ISMR) is more important than their individual impact because both the oscillations exist simultaneously throughout the year. To represent the simultaneous impact of NAO and SO, an index called effective strength index (ESI) has been defined on the basis of monthly NAO and SO indices. The variation in the tendency of ESI from January through April has been analyzed and reveals that when this tendency is decreasing, then the ESI value throughout the monsoon season (June-September) of the year remains negative and vice versa. This study further suggests that during the negative phase of ESI tendency, almost all subdivisions of India show above-normal rainfall and vice versa. The correlation analysis indicates that the ESI-tendency is showing an inverse and statistically significant relationship with rainfall over 14 subdivisions of India. Area wise, about 50 of the total area of India shows statistically significant association. Moreover, the ESI-tendency shows a significant relationship with rainfall over north west India, west central India, central north east India, peninsular India and India as a whole. Thus, ESI-tendency can be used as a precursor for the prediction of Indian summer monsoon rainfall on a smaller spatial scale.